The present invention relates to a copier, printer, facsimile apparatus or similar image forming apparatus of the type including a blade for removing a developer left on a photoconductive element or similar image carrier.
An image forming apparatus of the kind described includes a photoconductive drum or similar image carrier driven by drive means. Latent image forming means uniformly charges the surface of the drum and then exposes it in accordance with a document image or an image signal, thereby forming a latent image on the drum. A developing device develops the latent image with a developer to thereby produce a corresponding toner image. An image transferring device transfers the toner image from the drum to a paper or similar recording medium. A cleaning device removes the developer left on the drum after the image transfer. A fixing device fixes the toner image on the recording medium.
While a heat roller and a press roller included in the fixing device are rotated by a drive source, at least the heat roller is heated by a heater. As a result, when the paper is brought to a nip between the two rollers, the toner image is fixed on the paper by heat and pressure. In a high-speed image forming apparatus whose heat roller has a substantial wall thickness, the heat roller and press roller are rotated in a preliminary rotation mode after the power-on of the apparatus, but before the beginning of image formation. This evenly distributes the surface temperature of the heat roller. Usually, during the preliminary rotation mode relating to fixation, the developing device is not operated. In addition, in this mode of operation, the heat roller and press roller are continuously rotated for a long period of time (sometimes more than 5 minutes).
The cleaning device is often implemented by a blade cleaning scheme using a blade. The blade is held in contact with the photoconductive drum in order to scrape off the developer left on the drum after the image transfer. The problem with this type of cleaning device is that friction acting between the drum and the blade is apt to cause the blade to be turned over or chipped, resulting in defective images. To solve this problem, toner must be fed between the drum and the blade for enhancing lubrication. Various methods have heretofore been proposed to feed toner between the drum and the blade in an image forming mode in which an image is formed in the usual manner. However, a method of feeding toner between the drum and the blade in a non-image forming mode in which no images are formed has rarely been proposed.
Japanese Patent Laid-Open Publication No. 62-34172 teaches a method of feeding toner between the drum and the blade in the non-image forming mode. The object of this method is to make it needless to apply a lubricant around the drum when the drum is mounted to the apparatus. Specifically, a black solid image is formed over one half or the entire periphery of the drum and fed to the above position.
Japanese Patent Laid-Open Publication No. 61-95381 discloses a cleaning device for an image forming apparatus and including a cleaning blade movable into and out of contact with the surface of an image carrier. Only when a single image forming operation is not followed by the next image forming operation within a preselected period of time, the cleaning device is controlled such that toner is deposited on the surface of the image carrier before the subsequent image forming operation. Specifically, the above document teaches that a bias for development is applied to cause toner to deposit on the image carrier, and that some positively charged toner, which exists in negatively or regular charged toner is transferred to the image carrier by the bias for development.
Japanese Patent Laid-Open Publication No. 3-282486 proposes an image forming apparatus including an image carrier for forming a toner image thereon, drive means for driving the image carrier, nonvolatile store means for storing the duration of drive transmission from the drive means to the image carrier, and display means for urging the operator to replace the image carrier when the duration stored in the store means coincides with a preselected period of time.
Japanese Patent Laid-Open Publication No. 1-108592 pertains to a blade lubrication maintaining device of the type depositing toner on an image carrier between the end of a series of image forming cycles and the stop of an apparatus and thereby feeding it to a blade. The device is characterized in that toner amount control means is provided for controlling the amount of toner to deposit on the image carrier in accordance with the number of image forming cycles. This document teaches that the area of the image carrier for the toner to deposit or the density of the toner to deposit is controlled in accordance with the number of image forming cycles.
Further, Japanese Patent Laid-Open Publication No. 63-138369 relates to an electrostatic copier including an electrophotographic photoconductive element movable in a preselected direction, a corona discharger for charging the surface of the photoconductive element to a particular polarity, optics for projecting a document image onto the surface of the drum, a developing device for developing a latent image formed on the surface of the photoconductive element to thereby produce a corresponding toner image, predischarging means positioned upstream of the developing device in the above direction in order to dissipate the charge of the photoconductive element, a cleaning device including a n elastic blade for removing toner left on the photoconductive element after image transfer, and control means for controlling the predischarging means. The copier taught in the above document is characterized in that the control means controls the predischarging means such that toner slightly deposits on the photoconductive element over substantially the entire width of a non-image area where a toner image is not formed. Specifically, the predischarging means is implemented by a plurality of lamps arranged in the widthwise direction of the photoconductive element. The control means selectively turns off the lamps corresponding to the non-image area for a short period of time, so that toner slightly deposits on the above area of the photoconductive element due to charge left on the same area.
The method taught in the abovementioned Laid-Open Publication No. 62-34172 feeds toner between the drum and the blade during non-image formation. Therefore, this kind of toner feed occurs when frictional resistance between the drum and the blade is great, e.g., when the drum is newly mounted to the apparatus or replaced. Such a scheme is extremely effective when is rarely executed. However, assume that the toner is frequently fed, e.g., in the preliminary rotation mode occurring every time the fixing temperature is lower than a preselected temperature at the time of power-up of the apparatus; because development does not occur, the blade is likely to be turned over due to the absence of toner between the drum and the blade and the long duration of rotation of the heat roller and press roller. Then, there are brought about the scattering of toner, defective cleaning of the drum, and wasteful toner consumption. In addition, when charging means for charging the drum is implemented as a charge roller contacting the drum, the defective cleaning of the drum, for example, results in the smearing of the charge roller and therefore defective images.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Patent Laid-Open Publication No. 8-6441.